Several retinal conditions, such as proliferative diabetic retinopathy, diabetic macular edema, and retinal venous occlusive diseases, respond well to retinal photocoagulation treatment. In fact, panretinal photocoagulation (PRP) is the current standard of care for proliferative diabetic retinopathy. Retinal photocoagulation procedures frequently require delivery of a large number of laser doses to the retina. For example, PRP typically requires laser treatment of at least 1500 locations. Retinal photocoagulation is typically performed point-by-point, where each individual dose is positioned and delivered by the physician. Typically, laser spots range from 50-500 microns in diameter, have pulse durations of 100-200 ms and have a beam power of 200-800 mW. Laser wavelengths are typically green, yellow or red, although occasionally infrared radiation is used. Point by point treatment of a large number of locations tends to be a lengthy procedure, which frequently results in physician fatigue and patient discomfort.
Various approaches for reducing retinal photocoagulation treatment time have been developed. Some approaches are based on taking an image of the retina to be treated, planning and aligning all treatment locations with reference to the retinal image, and treating all of these locations automatically. A tracking system is usually required in these approaches to ensure alignment between planned treatment locations defined on the image and actual treatment locations on the retina. Such tracking systems must process large amounts of data in real time, and therefore tend to be complex and difficult to implement. A representative discussion of such an approach is found in Wright et al., Journal of Biomedical Optics, 5 (1), 56-61, January 2000.
Other approaches provide multiple treatment laser beams to reduce treatment time. Multiple treatment beams can be provided by an optical beam-multiplier (e.g., U.S. Pat. No. 4,884,884 to Reis) or by an optical fiber having multiple closely spaced outputs (e.g., U.S. Pat. No. 5,921,981 to Bahmanyar et al.). Although these approaches are less complex than approaches based on retinal imaging and tracking, the treatment beam configurations cannot be easily or flexibly adjusted. For example, Reis discusses provision of a turret changer to permit selection of one beam multiplier from a set of several different beam multipliers. Such selection of one beam multiplier from a handful of beam multipliers is unlikely to provide the degree of flexibility desired in practice. Accordingly, there is a need for simple and flexible multi-location retina treatment that is not provided by known methods.